Unvented Flat Roof Assembly

In high wildfire areas vented roofs are a real problem because of burning embers being pulled into the vent causing the fires to spread lstiburek says.

Unvented flat roof assembly. Unvented flat roof assembly. Additionally an unvented roof assembly is safer in areas exposed to wildfires. Department of energy building america webinar high performance enclosure strategies. Before constructing a flat roof assembly please refer to the unvented roof assembly comments under 6 2 vented and unvented roof assemblies and if applicable 6 3 parapet walls.

Air permeable insulation such as fiberglass batts dense packed cellulose or blown in fiberglass can t be used alone for an unvented assembly since these types of insulation can allow moist indoor air to reach the cold roof sheathing leading to condensation or moisture accumulation. Unvented metal roof assemblies are common on warehouses factories and shopping malls. In the most recent issue of fine homebuilding martin holladay wrote a piece on insulating unvented roof assemblies. Roof assemblies must control for exterior moisture in a monolithic and complete fashion.

Condensing surface temperature controlled the thickness of the rigid insulation at both the roof deck and perimeter is determined by a calculation procedure similar to figure 5. The colder the climate the thicker the rigid insulation required. This presentation was delivered at the u s. Insulating unvented roof assemblies.

An unvented roof assembly is constructed without any ventilation and is fully sealed on all sides and filled with insulation. These assemblies are created by eliminating ventilation openings and moving the thermal moisture and air control boundaries to the plane of the roof deck. Joe lstiburek building science corporation subject. The most common way to eliminate venting from a roof assembly is to use a spray foam spf insulation.

Unvented roof assemblies such as conditioned attics and unvented cathedral ceilings are becoming common in north american construction. Unvented roof systems and advanced framing strategies created date. We re big fans of fine homebuilding. Foam free don t stay stuck in the sci finightmare of foam foam foam.

Unvented roof assemblies author. We agree that avoiding sheathing rot is critical and that air permeable insulation such as fiberglass or cellulose cannot be used alone. The higher the interior moisture level the thicker the. An unvented assembly can perform well but it s important to get the details right to avoid sheathing rot.

In unvented flat or low slope roofs with parapets perform a full flood test to ensure leak free installation of roofing membrane.